Preparation of cyclic alcohols by oxidation in the presence of boric acid



United States Patent The present invention relates to certainimprovements in the preparation of cyclic alcohols by oxidizingsaturated cyclic hydrocarbons with the aid of boric acid.

It is known that a saturated cyclic hydrocarbon may be oxidized to acyclic alcohol in the presence of boric acid. This oxidation is usuallycarried out in the liquid phase by contacting the hydrocarbon with a gascontaining molecular oxygen, for example, air, at a temperature of100300 C. The formation of undesired b-y-products, such as acids, ispartly counteracted by the reaction of the boric acid with the alcoholsformed to yield esters which resist further oxidation. This favorableactivity of boric acid, which is rather hard to dissolve in thehydrocarbon to be oxidized, can be promoted by suspending the solidboric acid in the hydrocarbon in a finely divided state. To this end,the boric acid crystals may first be ground in .a mill and screened,after which the resulting fine powder can be distributed in thehydrocarbon.

As will be appreciated, this pretreatment of the boric acid, includinggrinding and screening, is quite complicated and there are attendantlosses of acid. Accordingly, the principal object of the presentinvention is to provide a novel Way of preparing a finely dividedsuspension of boric acid in the hydrocarbon which is free from theindicated prior difiicul-ties. Another object of the invention is toprovide a simplified procedure for preparing the desired boric acidsuspension in hydrocarbon. A more specific object is the provision of aprocess tor oxidizing cyclic hydrocarbons to give high yields of cyclicalcohols. A further specific object is to avoid the complicated boricacid pre-treatment and attendant losses of acid encountered in priorprocedures. Other objects will also be apparent from the followingdetailed description of the invention.

Broadly stated, the objects of the invention are realized by utilizingfor the oxidation reaction herein involved, a suspension of boric acidin hydrocarbon which has been prepared by mixing the hydrocarbon with anaqueous solution of boric acid and the-n evaporating the water from thismixture.

The amount of boric acid utilized can be varied and should be related tothe amount of alcohol formed so that the alcohol can be bound as anester. Desirab-ly an excess of the acid is used over that theoreticallynecessary to react with "all of the alcohol which is formed.

Thus, for example, if the hydrocarbon oxidation is to be terminated atan early stage Where there is only a low degree of hydrocarbonconversion, e.g., 5-25%, it is sufficient to use just a small amount ofboric acid, typically, -15% excess over that theoretically required toreact with all of the alcohol.

In preparing the boric acid suspension according to the presentinvention, it is preferred, because of the low solubility of boric acidin water, to use a hot, aqueous solution containing about to by weightof boric acid, the temperature of the solution usually being 40 to 60 C.

After the aqueous boric acid solution has been mixed with thehydrocarbon -(which is also desirably at a tem- 11 Claims.

3,287,423 Patented Nov. 22, 1966 rated along with the water can berecirculated after a phase separation. When the water is withdrawn fromthe mixture, the boric acid separates out in a very finely divided formand can be easily kept suspended in the hydrocarbon by stirring. Theamount of boric acid in the suspension may be varied by adding furtheramounts of hydrocarbon. Preferably, the resulting suspension comprisesfrom 5 to 15% by weight of boric acid although proportions outside thisrange may also be used.

The hydrocarbon is oxidized by bringing the suspension of boric acid inhydrocarbon at a temperature of 100300 C. into contact with molecularoxygen, e.'g., pure oxygen or a gas containing molecular oxygen, such asair or other mixtures of oxygen and inert gas, typically nitrogen. Thiscan be accomplished very simply by passing the gas through thesuspension. A catalyst is not necessary although one may be used ifdesired. Typical catalysts include cobalt n'ap-hthenate and cobaltoleate.

It is recommended that the boric acid be used together with a boric acidsalt, preferably an alkali-metal salt, such as potassium borate orborax. It has been found that during the oxidation the boric acid saltsreact with the acid try-products which are formed along with the alcoholto produce additional boric acid. The amount of boric acid salt used forthis purpose may be varied considerably. For example, the salt may beused in amount equivalent to the amount of boric acid used. Less saltmay also be used, typically, 10, 25, 40 or of the amount of acid.

The oxidation should be carried out under sufiicient pressure to keepthe hydrocarbon in the liquid phase during the oxidation. The actualpressure utilized in any particular situation will, of course, depend onthe oxidation temperature and the boiling point of the hydrocarbon. Atemperature of from C. to 300 C. is used, this being the customary range[for this oxidation.

The water formed in the oxidation is easily removed by evaporationduring the oxidation and any hydrocarbon evaporated along with the watercan be recirculated after condensation and phase separation. When theoxidation is completed, the nonconverted hydrocarbon can be recovered bydistillation and the desired alcohol can be recovered from the remainingreaction mixture by sasponitying the resulting esters by treatment withwater and/or alkali hydroxide.

The invention is illustrated but not limited by the following examples:

Example 1 A hot solution (temperature 50 to 55 C.) of 2 kg. of boricacid in 10 kg. of Water is mixed with 25 kg. of cyclohex-ane at atemperature of 50 to 55 C. in an autoclave with a capacity of 50 litresand provided with a stirrer. After that, water and cyclo-hexane areevaporated from the autoclave at a temperature of 68 to 75 C. until asuspension of solid boric .acid in cyclohexane is obtained. Followingcondensation and phase separation, the cyclohexane evaporated in thisoperation is returned to the autoclave.

The temperature of the suspension is then raised to 164165 C., and .agas consisting of nitrogen and oxygen (5% by volume of oxygen) is passedthrough the autoclave at the rate of 5 m. per hour (measured at 0 C. and1 atm.), the pressure being kept at 9 atm. The water formed during theoxidation is removed in the vapor state, while hydrocarbon evaporatedalong with the water is recirculated after condensation.

After 2 hours the oxidation is stopped, and the nonconverted cyclohexaneis separated oit by distillation. 23

kg. of cyclohexane are recovered, which corresponds to a degree ofconversion of 8% by Weight.

The raw oxidation product is washed with a diluted, aqueous sodiumhydroxide solution (0.5%) at a temperature of 60 to 90 C. Thisope-ration saponifies the esters which are present. Alfter repeatedWashing with water and phase separation, an oil containing 1.62 kg. ofcyclohexanol and 0.29 kg. of cyclohexanone (molar ratio about 5:1) isobtained. The boric acid and the resulting acid oxidation products arecontained in the water phase.

The yield, calculated on the amount of converted cyclohexane, amounts to68.3% of cyclohexanol and 13.7% of cyclohexanone.

Example 2 The oxidation described in Example 1 is repeated except that asolution of 3.5 kg. of boric acid in 20 kg. of water is used to preparethe suspension and the oxidation is continued for 4 hours.

The result is:

Recovered cyclohexane 21 kg.; degree of conversion 16%.

Cyclohexanol, 3.06 kg; yield 64.4%. Cyclohexanone, 0.50 kg.; yield10.7%. Molar ratio cyclohexanolzcyclohexanone=6: 1.

Example 3 The oxidation described in Example 1 is repeated except that asolution of 2 kg. of boric acid and 4 kg. of borax in 30 kg. of water isused in preparing the suspension.

After the oxidation has been continued for 2 hours, the result is:

Recovered cyclohexane 22.74 kg; degree of conversion Cyclohexanol, 2.02kg.; yield 74.3%.

Cyclohexanone, 0.28 kg.; yield 10.6%.

Molar ratio cyclohexanol: cyclohexan one=7: 1.

Example 4 The oxidation described in Example 1 is repeated except thatthe oxidation pressure is maintained at 30 atm. The stirrer in theautoclave is a propeller stirrer rotating in a tube which producesintensive agitation. The oxidation is continued for 4 hours.

The result is:

'Recovered cyclohexane 21.3 kg; degree of conversion 15%. Cycl-ohexanol,2.94 kg; yield 78%. Cyclohexanone, 0.36 kg; yield 9.6%. Molar ratiocyclohcxanol:cyclohexanone=8.2: 1.

As will be apparent from the foregoing examples, the oxidation reactiongive-s esters which are saponified or hydrolyzed by heating with water,aqueous sodium hydroxide or the like to give the desired alcohols. Thisgives a two phase system, i.e., an oil phase containing the alcohol anda water phase which as boric acid dissolved therein. These two phasescan be readily separated from each other by phase separation.

The aqueous boric "acid solution which is obtained by the phaseseparation referred to in the preceding paragraph may be used to prepareboric acid suspension sub these include such valuablealkane-dicarboxylic acids as succinic acid, glutaric acid, adipic acidand higher alkanedicarboxylic acids. According to another aspect of theinvention, it has also been found that these acid byproducts can beeffectively removed from the aqueous boric acid solution by means of abasic anion exchanger so as to leave an aqueous solution of boric acidwhich is suitable for reuse. The ion exchanger'may be any anionexchanger containing active amine groups or quaternary ammonium groupssuch as the so-called amberlite exchangers and permutite exchangers.

After removing the acid -lay-products, the aqueous boric acid solutionis mixed with hydrocarbon as aforesaid for the purpose of preparing aboric acid suspension in hydrocarbon suitable for oxidation. To thisend, it is usually preferred, in order to minimize hydrocarbonevaporation and to avoid evaporating large amounts of water after thesolution has been mixed with hydrocarbon, to first evaporate the aqueoussolution of boric acid to a smaller volume, preferably until a boricacid solution is obtained which is saturated at a temperature of 40 toC. and to then mix this concentrated solution with the hydrocarbon. Thishas the additional advantage that any volatile by-prod-ucts contained inthe aqueous solu tion, such as monocarboxylic acids, can be removed in asimple way by the concentrating step. The volatile byproducts may alsobe removed by evaporating the aqueous solution before it is brought intocontact with the ion exchanger so as to minimize the load on the ionexchanger.

As indicated above, the oxidation reaction product can be convenientlysaponified or hydrolyzed by heating it with water at, for example, atemperature of 60 to C., with simultaneous stirring. Substances givingan alkaline reaction, such as the alkali metal carbonates as well as thealkali metal hydroxides as previously mentioned, may also be used.

If the resulting oil phase contains esters that have not yet beenhydrolyzed, this phase may be re-subjected to a hydrolysis treatment andthe resulting alcohol can be recovered if necessary after distillation.In addition to the cyclic alcohol, the oxidation reaction productusually contains the corresponding cyclic ketone, in amounts of appr. 6to /1 of the amount by Weight of cyclic alcohol.

If alkaline substances are used in the hydrolysis, it will be recognizedthat metal ions will be present in the aqueous phase which is separatedfrom the alcohol oil phase. These metal ions can be removed by means ofan acid cation exchanger but if the boric acid is used together with aboric acid salt, at least some of these metal ions may be retained inthe aqueous phase.

The additional features of the invention as discussed above are furtherillustrated by the following:

Example 5 A hot solution (temperature 80 to 85 C.) of 2 kg. of boricacid in 7 kg. of water is mixed with 25 kg. of cyclohexane in anautoclave, having .a capacity of 50 liters and provided with :a stirrer,at a temperature of 80 to 85 C. and a pressure of 25 atm. After that,water and cyclohexaue are evaporated from the autoclave at a temperatureof to C. until a suspension of solid boric acid in cyclohexane results.The evaporated cyclohexane is returned to the autoclave aftercondensation and phase separation.

The temperature is then raised to 164-165" C., and a gas consisting ofnitrogen and oxygen (5% by volume of oxygen) is passed through theautoclave at the rate of 5 in. per hour (measured at 0 C. and 1 atm.),the pressure being kept at 25 atm. The water formed during oxidation isremoved in the vapor state, while hydro carbon evaporated along with thewater is recirculated after condensation.

After 2 hours the oxidation is stopped, and the non convertedcyclohexane separated 01f by distillation. 23

kg. of cyclohexane are recovered, which corresponds to a degree ofconversion of 8% by weight.

The raw oxidation product is mixed with 20 kg. of water and hydrolyzedat a temperature of 80 to 90 C. with simultaneous stirring, after whichthe oil is separated from the aqueous phase. From the oil obtained 1.62kg. of cyclohexanol (yield 68.3%) and 0.29 kg. of cyclohexanone (yield13.7%) are recovered. The yields are calculated to the amount ofconverted cyclohexane.

The aqueous phase is evaporated until a boric acid solution resultswhich is virtually saturated at a temperature of 60 to 65 C. The vapordischarge during the evaporation is condensed, the condensate containingsmall amounts of alkane monocarboxylic acids, cyclohexanol, andcyclohexanone. After that, the evaporated boric acid solution is passedthrough a column containing permutite (1.5 litres) at a temperature of60 to 65 C.

At a temperature of 80 to 85 C. the aqueous solution is then furtherevaporated to 9 kg., in which 2 kg. of boric acid are present. Thisboric acid solution is re-used by mixing with additional hydrocarbon,evaporating off the water to obtain a boric acid suspension inhydrocarbon and subjecting this suspension to oxidation as aforesaid.

The anion exchanger is regenerated by passing dilute nitric acid throughit at a temperature of 60 to 65 C. As a result, an aqueous solution ofalkane dicarboxylic acids is obtained, the solution being advantageouslyevaporated to dryness.

As a further feature of the invention, it has been found that, in lieuof subjecting the aqueous phase obtained by hydrolyzing the oxidationreaction product to treatment with ion exchanger, the aqueous phase maybe directly mixed with hydrocarbon to be oxidized after which the waterand volatile carboxylic acids, mainly the lower alkane monocarboxylicacids, are evaporated from the resulting mixture. This is usuallyaccomplished at a temperature of about 100 to 110 C. until all of thewater is evaporated. Any hydrocarbon which is also evaporated along Withthe water and volatile carboxylic acids may be recirculated aftercondensation. Evaporation causes the boric acid to precipitate and thisis then separated from the hydrocarbon in any convenient fashion, e.g.,by filtration or centrifuging. The hydrocarbon retains in solution thenon-volatilized carboxylic acids, mainly alkanedicarboxylic acids suchas succinic acid, glutaric acid, adipic acid and higheralkanedicarboxylic acids. These acids may be extracted from thehydrocarbon with water and can be readily recovered from the resultingaqueous solution. The boric acid, previously precipitated and separatedfrom the hydrocarbon may be dissolved in water, the resulting solutionmixed with the hydrocarbon and this mixture appropriately processed byevaporating water to prepare the boric acid suspension in hydrocarbonfor oxidation.

The following example illustrates the alternative procedure referred toin the preceding paragraph:

Example 6 A hot solution of 2 kg. of boric acid in 8 kg. of water ismixed with 25 kg. of cyclohexane at a temperature of 80 to 85 C. and apressure of 25 atm. in an autoclave with a capacity of 50 litres. Theautoclave is provided with a propeller stirrer which rotates in a tube,as a result of which intimate mixing is achieved. After that, water andcyclohexane are evaporated from the autoclave at a temperature of 100 to110 C. until a suspension of solid boric acid in cyclohexane has beenobtained. Following condensation and phase separation, the cyclohexaneevaporated in this step is returned to the autoclave.

The temperature is then raised to 164165 C., and a gas consisting ofnitrogen and oxygen (5% by volume of oxygen) is passed through theautoclave at the rate of 5 111. per hour (measured at 0 C. and 1 atm.),the pressure being kept at 25 atm. The water formed during the oxidationis removed in the vapor state, while hydrocarered. These yields arebased on the amount of converted cyclohexane.

The aqueous phase is mixed with the 21.5 kg. of recovered cyclohexane,and water and volatile carboxylic acids are removed from the mixture byevaporation, while the cyclohexane evaporated along with thesesubstances is recirculated after condensation. The solid boric acid (2kg.) precipitated in this operation is separated off.

The carboxylic acids present in the cyclohexane are extracted withwater. The aqueous carboxylic acid solution is evaporated to dryness andthe cyclohexane purified in this way is returned to the autoclave, wherethe amount is made up to 25 kg., while the boric acid previouslyseparated off is dissolved in 8 kg. of water, and also introduced intothe autoclave to prepare additional boric acid suspension in cyclohexanefor further oxidation.

While the foregoing examples are directed specifically to the oxidationof cyclohexane, the invention is not restricted thereto and othersaturated cyclic hydrocarbons may also be similarly oxidized into theappropriate alcohols. Thus, for example, the process herein may be usedto oxidize such other saturated cyclic hydrocarbons as cyclopentane,cycloheptane, cyclo-octane and cyclododecane to give the correspondingcyclic alcohols.

Other modifications may be made in the invention described herein.Hence, the scope of the invention is set forth in the following claimswherein:

What is claimed is:

1. In a process for the preparation of a cyclic alcohol by the oxidationof a saturated cyclic hydrocarbon selected from the group consisting ofcyclopentane, cyclohexane, cycloheptane, cyclooctane and cyclododecaneby preparing a suspension of boric acid in said hydrocarbon and thencontacting said suspension with molecular oxygen at a temperature of to300 C. followed by hydrolysis of the resulting oxidation product, theimprovement Which comprises preparing said suspension by mixing saidhydrocarbon with an aqueous solution of boric acid and then evaporatingall of the water from said mixture to leave behind a suspension of solidboric acid in said hydrocarbon.

2. The process of claim 1 wherein said aqueous solution of boric acidincludes a boric acid salt.

3. The process of claim 2 wherein said salt is an alkali metal borate.

4. The process of claim 1 wherein said aqueous solution contains 15 to20% by weight of said acid and said solution is mixed with hydrocarbonat 40 to 60 C.

5. The process of claim 4 wherein said hydrocarbon is cyclohexane.

6. The process of claim 1 wherein the amount of acid used is in excessof the amount of alcohol formed.

7. The process of claim 1 wherein said oxidation reaction product ishydrolyzed to give an oil phase containing the desired alcohol and anaqueous phase containing boric acid and acid by-products, said acidby-products being removed from said aqueous phase by contacting saidaqueous phase with a basic anion exchanger.

8. The process of claim 7 wherein the aqueous boric acid phase afterremoval of said acid by-products is mixed with hydrocarbon to prepareadditional suspension for said oxidation.

9. The process of claim 8 wherein water is evaporated from said aqueousphase before mixing with the hydrocarbon, said evaporation continuinguntil a boric acid solution is obtained which is saturated at atemperature of 40 to 85 C. p

10. The process of claim 1 wherein said oxidation reaction product ishydrolyzed to give an oil phase containing the desired alcohol and anaqueous phase containing boric acid, followed by separating said phases,then mixing said aqueous phase directly with hydrocarbon and evaporatingthe water from the resulting mixture whereby boric acid is precipitatedin said hydrocarbon, recycling any hydrocarbon evaporated with saidwater, separating the precipitated boric acid from said hydrocarbon,recovering by-product carboxylic acids from said hydrocarbon byextraction with water and utilizing the boric acid 8 11. The process ofclaim 10 wherein said separated boric acid is dissolved in water, theresulting solution mixed with hydrocarbon and water thereafterevaporated from said mixture to prepare said suspension.

References Iited by the Examiner UNITED STATES PATENTS 1,947,989 2/1934Hellthaler 260-631 2,385,546 9/1945 Smith 260638 10 3,109,864 11/1963Fox et a1. 260-631 LEON ZITVER, Primary Examiner.

LORRAINE A. WEINBERGER, Examiner.

separated from said hydrocarbon to prepare additional 15 1G. DILLAHUNTYAssistant Examiner.

suspension for use in said oxidation.-

1. IN A PROCESS FOR THE PREPARATION OF A CYCLIC ALCOHOL BY THE OXIDATIONOF A SATURATED CYCLIC HYDROCARBON SELECTED FROM THE GROUP CONSISTING OFCYCLOPENTANE, CYCLOHEXANE, CYCLOHEPTANE, CYCLOOCTANE AND CYCLODODECANEBY PREPARING A SUSPENSION OF BORIC ACID IN SAID HYDROCARBON AND THENCONTACTING SAID SUSPENSION WITH MOLECULAR OXYGEN AT A TEMPERATURE OF 100TO 300* C. FOLLOWED BY HYDROLYSIS OF THE RESULTING OXIDATION PRODUCT,THE IMPROVEMENT WHICH COMPRISES PREPARING SAID SUSPENSION BY MIXING SAIDHYDROCARBON WITH AN AQUEOUS SOLUTION OF BORIC ACID AND THEN EVAPORATIONGALL OF THE WATER FROM SAID MIXTURE TO LEAVE BEHIND A SUSPENSION OF SOLIDBORIC ACID IN SAID HYDROCARBON.